Cellular and Molecular Physiology Laboratory (CMPL) and Perinatology Research Laboratory (PRL), Division of
Obstetrics and Gynecology, School of Medicine, Faculty of Medicine, Pontificia Universidad Católica de Chile,
P.O. Box 114-D, Santiago, Chile; 2Vascular Physiology Laboratory, Department of Physiology, Faculty of
Biological Sciences, Universidad de Concepción, Concepción, Chile; 3Experimental Physiology Laboratory,
Department of Biomedicine, Faculty of Health Sciences, Universidad de Antofagasta, Antofagasta, Chile;
4
Department of Obstetrics and Gynecology, Clínica Dávila, Santiago, Chile and 5Division of Obstetrics and
Gynecology, School of Medicine, Faculty of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
Abstract: Molecular mechanisms are increasingly being reported allowing a better understanding of the mother health
and fetal metabolic abnormalities in pregnancies that are affected by diseases. Most aspects of cellular function are
regulated by a tuned equilibrium between the ability of cells to synthesize oxidants and antioxidants, and preventing
the formation or blocking the actions of antioxidants. Oxidative and nitrative stresses are causative agents in human
pregnancy-related disorders, including preeclampsia, intrauterine growth restriction, pre-gestational and gestational
diabetes and premature delivery. An equilibrium between abundance and/or activity of reactive oxygen (ROS) and
nitrogen (RNS) derived species, and antioxidant and nitrative enzyme systems are crucial in gestation. Hydrogen
peroxide and superoxide radicals as well as NADPH oxidase and nitric oxide synthases (NOS) play significant
contributions to maintain this physiological equilibrium in the human fetoplacental endothelium. Alterations in this
relationship lead to abnormal cell function, where the endothelium is one of the targeted cells affected by these
pathological conditions. Thus, altered ROS and RNS production, i.e., over the physiological permitted levels, leads to
altered endothelial function, a phenomenon associated with endothelial dysfunction in pregnancy diseases. This
chapter briefly reviews general aspects of oxidative and nitrative stress in the vasculature in diseases of pregnancy, and
a role to NADPH oxidase, NOS and adenosine is summarized.

evidenced in the unequal therapeutical approach that is at present used to treat patients with these pregnancy-related
pathologies associated with placental dysfunction.
The normal development of the placenta is crucial to sustain the adequate fetal development and growth. The human
feto-placental circulation under physiological conditions exhibits a high blood flow and low vascular resistance.
Since it lacks of autonomic innervation [7,8], circulating and locally released vasoactive molecules, such as nitric
oxide (NO), are crucial to maintain the control of feto-placental hemodynamics [5,6]. The alteration in this process,
where the placental function is not preserved, referred as ‘placental dysfunction’, leads to different clinical
manifestations of diseases of pregnancy diagnosed alone or associated with other diseases in a same patient, leading
to multiple clinical possibilities, maternal and/or fetal symptoms, as well as different short and long term prognosis.
Oxidative stress has been suggested as a causative agent in human pregnancy-related disorders, such as embryonic
resorption, recurrent pregnancy loss, PE, IUGR and fetal death [5, 9]. It has been suggested that reactive oxygen
species (ROS) and antioxidant enzyme systems are important for reproduction and gestation. For example, hydrogen
peroxide (H2O2) and superoxide radicals, such as the superoxide anion (O2-), play important roles in the control of
uterine contraction [10,11], and in implantation and development of the fetus. In these phenomena a fine regulation
of ROS levels by oxidases and antioxidant enzymes activity in cells from placental tissues is seen. Several markers
of oxidative stress like higher levels of pro-inflammatory cytokines, 8-isoprostane, H2O2 and O2- in the plasma and
the placenta have been detected in PE [9]. Although measurements of markers of oxidative stress in maternal blood
and urine show that pregnancy per se is a state of oxidative stress, this is heightened in pregnancies complicated by
PE, IUGR or diabetes [3, 5]. Placenta production of O2- is increased in PE and there is evidence for an increase in
O2- production in the placenta that is dependent on homologues of the cytochrome subunit of the phagocyte
NADPH oxidase (NOX) [12]. Nox1 and Nox5 isoforms of the NOX family were initially cloned in human
trophoblast, and the expression of these isoforms increased in the syncytiotrophoblast, vascular endothelium and
estromal cells of the placenta in PE [5,13], suggesting that these isoforms could be required for the state of
‘oxidative stress’ in this pathology [3, 5]. In addition to ROS, it has been shown that in maternal circulating
leucocytes from 16th week of gestation there is an elevation of nitrative stress. The prolonged nitrative stress in GD
patients may be involved in the development of carbohydrate intolerance later in life or in the development of late
cardiovascular complications [14]. In patients with GD or PE there is a decrease in the antioxidant defense
paralleled by increased levels of protein oxidation markers associated with oxidative stress [15]. In addition, in
placental endothelial cells from PE there is a decrease in the expression of the inducible NO synthase (iNOS)
isoform related with high levels of extracellular adenosine and oxidative stress. This phenomenon could be involved
in the reduced placental blood flow in PE where a pivotal role seems to be played by vascular macro and
microvascular endothelium [3, 4, 6].
Vascular Function and Reactive Oxygen (ROS) and Nitrative (RNS) Species
Endothelial cells are involved in regulation of vascular tone through the release of vasoactive substances, such as
prostacyclins (PGI2) [16], endothelin-1 [17] and NO [16,18]. The broad functions of NO include regulation of
vascular tone, cell proliferation, vascular remodeling, inflammation and thrombotic balance [19,20]. In other hands,
ROS are important vascular signaling molecules or mediators of oxidative stress [21]. ROS modulate signaling of
growth factors and transcription factors controlling gene expression associated with proliferation, differentiation and
apoptosis. Under normal physiological conditions, ROS degradation by antioxidant enzymes is enough to maintain a
controlled activation of signaling cascades (Fig. 1).
ROS include a number of highly chemically reactive molecules including O2•-, hydroxyl radical (•OH), peroxide
radicals (ROO•), carbon monoxide (CO), and certain non-radicals molecules that are either oxidizing agents and are
easily converted into radicals, such as hypochlorous acid (HOCl), ozone (O3), singlet oxygen (1O2) and hydrogen
peroxide (H2O2) [22]. The O2•- can be synthesized by NOX, xanthine oxidoreductase (XOR), complexes I and III of
the electron transport chain, uncoupled NOS [19], heme-oxygenase (HO), the P450 enzymes family and enzymes of
the arachidonic acid metabolism [23]. NOS synthesize O2•- only when adopt the "uncoupled" form due to several
conditions including reduced availability of cofactors such as tetrahydrobiopterine (BH4) (Fig. 1).
In addition, reactive nitrative species (RNS) relates mainly to NO•, which is synthesized by NOS in normal
conditions, but depending on its environment, it can be transformed into other species such nitrosonium cation

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(NO+), nitroxyl anion (NO-) and peroxynitrite (ONOO-) [24]. The latter could also be considered as ROS since is the
product of a reaction between NO and O2•-. Similarly, there are several antioxidant systems that control the potential
damage that could produce an environment of oxidative stress. Non-enzymatic antioxidant mechanisms are
important in the defense or protection against the deleterious effects of oxidative agents. Examples of these
molecules include ascorbic acid (vitamin C), α-tocopherol (vitamin E) and glutathione (GSH). GSH is the major
cellular redox buffer and its intracellular concentration is in mM range [25]. In addition, cells express enzyme
systems to control oxidative stress, such as superoxide dismutase (SOD), which converts O2•- into H2O2 and O2.
SOD uses metals as cofactors (Zn and Cu in the cytoplasm, and Mn in the mitochondria). Glutathione peroxidase
(GPx) catalyzes the reduction of H2O2 oxidizing GSH to oxidized glutathione (GSSG), which oxidizes cysteine
residues of proteins [26], a modification referred as S-glutathiolation. Catalase (CAT) metabolizes H2O2 to form O2
and H2O. Thus, cells handle abnormal increases in ROS under stress conditions; however, in pathological
circumstances the antioxidant capacity is exceeded by oxidative stress leading to cell damage.
Physiological

O2

Pathological at high concentration

e-

NOX
Uncoupled NOS
XO
METC

NOS

L-Arginine

O2•-

+ NO

SOD

ONOO-

H2O2
GSH
CAT

GR

GPx

GSSG

H2O

+ O2

H2O

Protein nitration
Lipid peroxidation
DNA oxidation

Altered cell function

Figure 1: Enzyme systems involved in the generation and control of oxidative and nitrative stress. Overproduction of superoxide
anion (O2.-) by NADPH oxidases (NOX), uncoupled nitric oxide synthase (NOS), xanthine oxidase (XO) and mitochondrial
electron transport chain (METC) and further reaction with nitric oxide (NO) results in the formation of peroxynitrite (ONOO-),
which changes several molecules in the cell leading to altered cell function. On the other hand, O2- accumulation is avoided by
the action of superoxide dismutase (SOD) that converts it into hydrogen peroxide (H2O2), which is finally degraded into water by
catalase (CAT) and glutathione cycle system preventing cell damage. Light blue shows a physiological condition, while red
refers to pathological conditions due to abnormally elevated levels. GSH, glutathione; GSSG, glutathione disulfide; GPx,
glutathione peroxidase; GR, glutathione reductase.

SYNTHESIS OF ROS IN THE VASCULAR ENDOTHELIUM
Among all sources of endothelial ROS, NOX are the only enzymes whose primary function is the generation of ROS
and play an important role in redox signaling [27]. The activity of NOX may cause uncoupling of eNOS as a secondary
effect to the oxidative degradation of tetrahydrobiopterin (BH4), leading to the synthesis of O2- in detrimental of NO
synthesis [28,29], a phenomena implicated in hyperglycemia-associated oxidative stress [30] (Fig. 2).
Once synthesized, O2- it is used as a substrate by SOD to generate H2O2 which has greater stability and capacity to
cross biological membranes and act as a modulator of signal transduction pathways [31]. In addition, the O2- reacts
rapidly with NO to generate ONOO- [32], a powerful oxidizing agent that induces DNA fragmentation and lipid
oxidation [33]. Currently, it is postulated that the mechanism by which oxygen ‘hijack’ the NO plays a central role
in the development of endothelial dysfunction in diseases such as diabetes mellitus [34-36], PE [3,37] and
hypertension [38]. In diabetes, it has been reported that activation of NOX is dependent of the protein kinase C
(PKC) activation [39], advance glycation-end products (AGEs) and angiotensin II [30]. The mechanism by which
NOX-derived ROS causes biological effects include stimulation of angiogenesis [40], activation of phospholipase
A2 [41], and increased PKC [42] and nuclear factor ĸB (NFĸB) [43] activity.

Maternal and Fetal Vascular Oxidative and Nitrative Stress

An Overview of Association with Oxidative Stress 101

Placenta endothelium
NADPH oxidase

XO

O2

Mitochondria

eNOS
O2

O2.-

BH 4
L-Arginine

O2

NO
ONOO-

H2O + O2

O2
L-Arginine

Catalase

H 2O

Uncoupled

Glutathione
peroxidase

H2O2

Protein nitration

Alterations in protein
function
Cellular signaling

Alterations in gene
expression

Endothelial
dysfunction

Figure 2: Sources of oxidative stress in the human fetoplacental endothelium. In endothelium exposed to a stressful situation
(grey arrows) there is an up regulation of NADPH oxidase and xanthine oxidase (XO), increased mitochondrial activity and/or
altered (uncoupling) function of the endothelial nitric oxide synthase (eNOS) due to reduced supplementation of
tetrahydrobiopterin (BH4) or L-arginine. This phenomenon leads to increased synthesis of superoxide anion (O2-) in detrimental
of nitric oxide (NO) synthesis. With a physiological L-arginine and cofactors availability to eNOS, this enzyme releases NO,
which in the presence of elevated levels of O2- is converted into peroxynitrite (ONOO-). The latter is a highly reactive molecule
involved in protein nitration leading to altered function in several proteins in vascular endothelium of the human fetoplacental
circulation. Alternatively an increase in the activity of superoxide dismutases (SOD) leading to synthesis of a more stable
reactive specie, hydrogen peroxide (H2O2), plays a role in regulation of intracellular signaling pathways involved in changes of
genes expression modifying expression of proteins involved in redox and NO metabolism. This phenomenon is accelerated if
there is a decrease in the activity of catalase and glutathione peroxidase. If these phenomena are chronic, endothelial dysfunction
and vascular damage in placental and fetal vessels is the final result.

Several studies indicate that persisting oxidative stress renders endothelial NOS (eNOS) dysfunctional, such that it
ceases to produce NO and produces O2- instead [19,22]. Pro-oxidant action of NO is attributed to reactive nitrogen
intermediates rather than NO itself [9]. In addition to the interaction with NO, ROS have important direct effects
through the modulation of diverse redox-sensitive pathways in endothelium [29]. In human umbilical vein
endothelial cells (HUVEC), ROS pathway mediated by the activity of NOX is involved in the cellular effect of high
extracellular concentration of D-glucose, related with changes in the expression and activity of proteins involved in
the L-arginine transport and NO synthesis [44]. The cellular damage induced by ROS in the endothelium generates a
reduced bioavailability of NO, leading to endothelial dysfunction [45-48]. If these alterations are maintained for
long periods of time (i.e., chronically), endothelial dysfunction resulting of this condition is associated with
structural alterations in blood vessels resulting in altered vascular tone, remodeling the vascular wall, platelet
aggregation and inflammation. All these phenomena would trigger clinical complications such as myocardial
infarction, heart attack, ischemia and cardiac congestive failure [20, 49].
In the vasculature, the major sources of O2- come from the activity of membrane and intracellular oxidases (NOX,
XOR), mitochondrial activity and the uncoupled eNOS. NOX complexes, the major molecular sources of O2-,
consist of four essential subunits, membrane subunits gp91phox and p22phox and cytosolic subunits p47phox and
p67phox; in addition, a cytosolic subunit p40phox has also been described [50]. Among the gp91phox isoforms,
there is consensus that Nox2 and Nox4 are expressed in endothelium and that Nox1, Nox2 and Nox4 are expressed
in vascular smooth muscle cells (VSMC) [29, 50]. Recently, expression and activity of Nox5 has been reported in
endothelium and placental cells [5, 13], but its physiological role in these tissues remains to be established. In
arteries from placental chorionic plate, H2O2 causes an increase in vascular tone, an effect blocked by activation of
CAT [51]. Also, vitamin C decreases the contractile response of placental vessels to the thromboxane A2 mimetic
U46619 [51], a molecule that increases ROS levels, and SOD and CAT activity in vascular smooth muscle cells

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[52]. Similar effects has been described in umbilical vein and in the microcirculation of the human placenta,
suggesting a potential relation between oxidative stress and changes in the vascular tone leading to vasoconstriction
in a mechanism mediated by increases in ROS synthesis from oxidative enzymes and related with higher activity of
cellular antioxidant mechanism [5].
SYNTHESIS OF RNS AND PROTEIN NITRATION IN THE VASCULAR ENDOTHELIUM
NO Synthesis
NO is a gas synthesized in endothelial cells from the semi-essential cationic amino acid L-arginine [44, 53], which is
transported from the extracellular space into the endothelial cell by a family of cationic amino acid transporters (i.e.,
CATs) [44, 54-56]. In fact, there is evidence that NOS activity may depend on the ability of endothelial cells to take
up its specific substrate L-arginine via a variety of membrane transporters systems [44,57-60]. Endothelial cells
transport L-arginine through the transport systems y+, y+L, b0,+ and B0,+ [2,44,54,55,57]. NO is synthesized from Larginine in a metabolic reaction leading to equimolar formation of L-citrulline and NO [53, 55, 61]. This reaction
requires the activity of NOS, a group of enzymes conformed by, at least, three isoforms, i.e., neuronal NOS (nNOS
or type 1), inducible NOS (iNOS or type 2) and endothelial NOS (eNOS or type 3) [1,44,62]. The NO diffuses from
endothelium to vascular smooth muscle cells leading to cyclic GMP (cGMP)-dependent vasodilatation [55, 63]. In
vessels without innervations, as the distal segment of the umbilical cord [7, 8], vascular tone is regulated by the
synthesis and release of vasoconstrictors and vasodilators from endothelial cells [64,65]. Thus, quiescent endothelial
cells express a vasodilator, anticoagulant and anti-adhesive phenotype, whereas endothelial cells exposed to
physiological stress have pro-coagulant, pro-adhesive and vasocontractile properties [66]. The reduced ability of the
endothelium to stimulate vasodilatation mediated by NO is one of the events that triggers the endothelial
dysfunction, which is strongly correlated with cardiovascular risk factors [67] and with early states of chronic
diseases such as hypertension, hypercholesterolemia, diabetes mellitus, hyperhomocysteinemia, chronic renal
failure, chronic cardiac failure [45-47].
Protein Nitration
Nitronio ion derives from ONOO- and produces nitration of tyrosine residues in proteins, a reaction used as a marker
for ONOO- formation in vivo. A higher abundance of nitrotyrosine in proteins has been described in several
diseases, including GD [68] as well as in atherosclerotic lesions of human coronary arteries, post-ischemic heart, and
in the placenta of pregnancies with PE [69]. Equally, it has been proposed that cell death by apoptosis in response to
high extracellular D-glucose is associated with increased formation of nitrotyrosine in HUVEC [70], and formation
of ONOO- reduces mitochondrial activity in several cell types [53]. Interestingly, adenosine uptake is an essential
step protecting mitochondrial function against the deleterious effects of increased ONOO- in rat astrocytes [71].
Thus, potential alterations induced by ONOO- on adenosine transport capacity in endothelial cells could be
determinant limiting the attributed antioxidant role of adenosine [72-74].
It has been shown that although adenosine did not limit the formation of ROS, this nucleoside decreased the deleterious
cellular consequences produced by ROS in rat hippocampus slices [75]. This effect of adenosine occurs via different
adenosine receptors. In rats a protective effect of the A1 adenosine receptor agonist phenylisopropyl adenosine (PIA) in
brain oxidative stress has been shown [76], and in isolated rat hearts perfused with H2O2 a selective protective effect of A1
adenosine receptor activation with N6-cyclopentyladenosine (CPA) against the cardiac toxicity of H2O2, where the
presence of A2A receptor agonist CGS-21680 has no effect, was reported [77]. This antioxidant effect of adenosine is not
only in the presence of H2O2, since adenosine and A1 adenosine receptor stimulation with CPA attenuated ischemic
intestinal injury via decreasing oxidative stress, lowering neutrophil infiltration, and increasing reduced glutathione
content [78]. Moreover, in PC12 cells the A2A adenosine receptors activation prevented oxidative stress trough a PKAdependent pathway, thus possibly playing a role in preventing apoptosis [79]. In the human cell line HK-2 treated with
H2O2, adenosine protected against H2O2-induced injury through the activation of A1 and A2A adenosine receptors,
apparently through different signaling pathways, i.e., A1 adenosine receptors-associated protection involves pertussis
toxin-sensitive G proteins and PKC, whereas A2A adenosine receptors involves PKA [80]. A different signaling pathway is
described in adult rat cardiomyocytes, where adenosine protects mitochondria from oxidant damage in response to H2O2
through a pathway involving A2A adenosine receptors, Src tyrosine kinase, phosphatidyl inositol 3-kinase (PI3k)/protein
kinase B (Akt), eNOS and NO [81]. There is also evidence that adenosine is functionally involved in the regulation of

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An Overview of Association with Oxidative Stress 103

cardiac ROS production under physiological conditions. The knockout mice or pharmacological blockade of the A2A in
vivo was associated with cardiac ROS production by NOX through mitogen activated protein kinases (MAPK) activation
[82]. The latter group described that inhibition of A2A adenosine receptors with SCH58261, knockdown of A2A adenosine
receptors using siRNA in the endothelial cell line SVEC4-10 or using a knockout mice effectively inhibits basal and acute
angiotensin II-induced ROS production by Nox2 [83].
Since it has been proposed that extracellular levels of adenosine are mainly maintained in the physiological range by the
ability of endothelial cells to take up this nucleoside, nucleoside membrane transporters play a pivotal role in modulating
biological effects of this purine nucleoside [1,4,6]. Nucleoside transporters grouped into two families mediate extracellular
adenosine removal: equilibrative nucleoside transporters (ENTs) and concentrative nucleoside transporters (CNTs)
[1,4,6,84,85]. At present four members of the ENTs family of solute carriers (SLC29A genes) have been cloned from
human tissues (i.e., ENT1, ENT2, ENT3 and ENT4). Under physiological conditions, in primary cultures of HUVEC
adenosine transport is mainly (~80%) mediated by the human ENT1 (hENT1) [86, 87], and in a minor fraction (~20%) by
hENT2 [87,88]. hENT1 is a protein of 456 amino acids, encoded by SLC29A1, with apparent Km values in the range of
50-200 µM for purine and pyrimidine nucleosides transport. hENT2 is a protein of 456 amino acids, encoded by
SLC29A2. In addition to purine and pyrimidine nucleosides, hENT2 also transports nucleobases and exhibits apparent Km
values varying from 40 to 150 µM for adenosine. hENT1-mediated transport is inhibited by <1 µM nitrobenzylmercapto
purine riboside (NBMPR) while higher NBMPR concentrations inhibit hENT2-mediated transport [84,87,88].
Separating hENT1- and hENT2-mediated transport from overall adenosine transport has been essential to characterize
the kinetic transport parameters of these proteins when co-expressed in mammalian cells. hENT1 and hENT2 proteins
exhibit tyrosine residues that are phosphorylated to maintain its transport function [89]. However, it is unknown whether
these sites are nitrated and what would be the potential effects of nitration reactions in the transport activity of these
proteins [2,6]. The amino acid sequence of hENT1 and hENT2 contain tyrosine residues in the positions Y11, Y172, Y232
and Y234 for hENT1, and Y11, Y159, Y221, Y222 and Y350 for hENT2. There are not existing studies addressing the potential
nitration of these sites in hENT1 or hENT2 [4,6], thus we would expect that these sites will be nitrated in diseases where
NO synthesis is increased, such as GD [1,2,4,6,44]. In addition, whether nitration of tyrosine is a post-translational
modification associated with changes in transport function in HUVEC and in human placental microvascular endothelial
cells (HPMEC) from pregnancy diseases, including GD and PE, or in cells from normal pregnancies exposed to hypoxia
or hyperglycemia is at present a phenomenon without a clear answer. Since adenosine transport mediated via hENT1
(and potentially via hENT2) is under strong regulation by the activity of PKC and NO in primary cultures of HUVEC
[87,88,90-94] it is expected a potential nitration of these cell signaling proteins or other proteins (perhaps the proper
membrane transport proteins) in response to activation of these signaling molecules [2,4,6].
OXIDATIVE AND NITRATIVE STRESS IN PREGNANCY DISORDERS INTRAUTERINE GROWTH
RESTRICTION (IUGR)
This syndrome is generally defined as the inability of the fetus to reach its potential intrauterine growth, and
clinically defined as the estimated fetal weight under the 10th percentile [2]. IUGR has been associated with prenatal
disturbances, including fetal asphyxia, prematurity and neurological disabilities. Gathering the available information
regarding IUGR-induced long-term morbidity, known as ‘fetal programming’, we can at this point remark an
association of IUGR and chronic diseases such as obesity, dyslipidemia, hypertension, type 2 diabetes and coronary
disease. Studies in IUGR and placental dysfunction show that in primary cultures of HUVEC derived from this
syndrome there is a reduced uptake of L-arginine [58,88] related to down-regulation of the expression of hCAT-1
(isoform 1 of human CATs) mRNA and protein levels as well as membrane depolarization which represents one of
the proposed mechanisms explaining this phenomenon in IUGR. Only recently it has been shown that HUVEC
derived from IUGR pregnancies over-express arginase II, an enzyme that also metabolizes L-arginine, leading to a
functional competition for this substrate with eNOS, thus reducing NOS activity and NO levels [95]. These results
highlight the fact that altered L-arginine transport and NO synthesis in the placenta endothelium may be crucial in
the pathophysiological processes involved in the etiology of this disease in human pregnancy.
An elevated oxidative stress level and reduced antioxidant activity has been reported in placentas from pregnancies
with IUGR compared with normal pregnancies [2] (Fig. 3). In the placenta of women with preeclampsia and IUGR
there is an increase in nitrated protein tyrosine residues, which is correlated with higher generation of O2- forming

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González et al.

ONOO-. The ONOO- also causes oxidation of tyrosine residues, changes that could lead to activation, suppression or
have no effect on the function of nitrated proteins [96]. To date, it has been reported that nitration of human SOD by
ONOO- inhibits its activity [97], but ONOO- inhibits XO activity [98], thereby controlling the synthesis of additional
ONOO-. These posttranslational modifications might be relevant to placental dysfunction seen in IUGR. However, the
relationship between nitrated proteins and impaired placental function is still poorly understood [5]. Interestingly, it has
been reported that SOD expression in placentas from pregnancies with IUGR, is not significantly different from
placentas from normal pregnancies [99]. Other studies show that IUGR is associated with altered activity of SOD, GPx,
CAT and XO in human microvillus tissue explants, in addition to altered levels of these molecules at the fetal and
maternal plasma [100]. These findings are complemented with reports suggesting that reduced SOD activity correlates
with elevated concentrations of cadmium, arsenic and lead in placenta homogenates from IUGR pregnancies [101].
Interestingly, it has been possible to cause in vitro an increase in the formation of syncytial knots by hypoxia and
hyperoxia (1 and 20% O2, respectively) compared with normoxia (6% O2) or H2O2 treatment, which is similar to those
observed in placentas from IUGR. Thus, an oxidative stress stage is closely associated with placental dysfunction in
IUGR by still not very well characterized mechanisms involving ROS and/or RNS [2, 5, 102].
PRE-ECLAMPSIA (PE)
This syndrome refers to several vascular alterations characterized by maternal hypertension and proteinuria [103].
PE is a cause of maternal mortality, and one of the main causes of perinatal mortality and neurological sequelae as
well as prematurity [2,3,5]. PE is characterized by poor perfusion of the maternal and fetal circulations of the
placenta, which thus affects fetal growth and development, and, even though it is epidemiologically important, the
etiology of preeclampsia has not been clearly established [3,5,104]. PE is characterized by profound dysfunction of
the vascular endothelium, a phenomenon that could be secondary to oxidative stress [105]. There is abundant
evidence [5, 99, 106, 107] that placental function is altered in PE and reductions in total radical trapping antioxidant
capacities such as the scavenger activity of SOD and CAT, glutathione metabolism and/or vitamin E levels, as well
as an increase in lipid peroxides, are seen in preeclamptic [108] or diabetic patients [109] together with the presence
of nitrotyrosine residues [5] in villous tissue. The placenta may be exposed to intermittent perfusion causing
ischemia/reperfusion injury [110] mediated mainly through the generation of cytotoxic ROS [111]. Several studies
show increased production of ROS as well as RNS in preeclamptic placenta [112-114], and increased maternal [115118] and fetal [119-121] plasma level, which is a phenomenon thought to scavenge NO to decrease its
bioavailability [103,122] (Fig. 3). Interestingly, blocking ROS generation would be beneficial in PE improving the
deteriorated endothelial function [123], including the fetal and maternal vascular endothelium [2, 3, 6].
Since adenosine plays a key role as a vasoactive molecule leading to local vasodilatation in most vascular beds,
including placental vessels [1,4,6] and acts as antioxidant [55,57] a role has also been assigned to this nucleoside in
PE [100]. It has been shown that PE is associated with increased plasma adenosine concentration with the
subsequent alteration of endothelial cell function due to the biological actions of this nucleoside. Adenosine, likely
acting via A2A adenosine receptors increases intracellular cAMP level and reduces the nuclear factor κB (NF-κB)
binding to NOS2A promoter gene leading to reduced transcriptional activity of this gene and reduced expression of
iNOS in hPMEC [3]. This phenomenon could explain, at least in part, the reduced placental blood flow
characteristic of PE. The impact of the potential role of adenosine on the etiology of PE-induced feto-placental
endothelial dysfunction is strengthened when placental hypoxic lesions, a phenomenon well documented as a
condition increasing extracellular adenosine [6], are clinically manifested in this pathology. Thus, a mechanism
associated with altered adenosine handling by the feto-placental vasculature, particularly at the micro and
macrovascular placenta endothelium, has been proposed [4,6]. This concept could be the base for future design and
application of new therapeutic protocols considering adenosine and its several biological effects, including its
potential as antioxidant (a very poorly documented property) and as pro-angiogenic factor in the placenta, in the
critical care of patients with preeclampsia to secure a less stressed development and growth of the fetus.
PRE-GESTATIONAL DIABETES
Pre-gestational diabetes is a state of endothelial dysfunction where ROS and RNS contribute to the progression of diabetes
[124,125]. Oxygen-free radicals including O2- are thought to result from prolonged periods of exposure to hyperglycemia
[44], a condition known to cause non-enzymatic glycation of plasma proteins [126]. The O2- in the absence of appropriate

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An Overview of Association with Oxidative Stress 105

levels of scavengers may lead to an imbalance between pro-oxidants and antioxidants and produce a state of oxidative
stress [4-6,44]. Diabetes mellitus type 2 (DMT2) is a chronic diseases leading to a high number of deaths resulting from
alterations of the endothelial dysfunction, and the World Health Organization, considering the gradual increasing in the
rates of obesity, aging and urbanization of world population, estimates that in 2030 the diabetes mellitus prevalence will
reach ~4.4% of the world population, increasing the number of people affected by this disease to more than 300 million
[127]. In addition, about 2.9 million people die annually from diseases whose origin is attributed to the development of
diabetes mellitus, being the vascular diseases the leading cause of morbidity and mortality in these patients [128,129].
Remarkable, it is well known that the development of diabetes in the pregnancy (i.e., gestational diabetes) has
repercussion in the development of DMT2 [130,131] or is associated with a high susceptibility to cardiovascular diseases
[4,132,133] later in life in both mother and child [2, 4, 6, 134].
The development of cardiovascular disease in diabetic patients is associated with increased oxidative stress [48]
caused by higher activity of the enzymes NOX and XOR, together with the uncoupling of eNOS. These phenomena
induce cell dysfunction through oxidation of lipoproteins, nucleic acids, carbohydrates and proteins [20, 48, 135].
However, prior to endothelial dysfunction and cardiovascular complications in diabetes mellitus, the greatest risk
factor is chronic hyperglycemia [6, 44, 129, 136, 137]. It has been shown that insulin resistance, resulting from
hyperglycemia, is present in metabolic and chronic diseases (i.e., obesity, hypertension and metabolic syndrome),
which increases the risk for developing cardiovascular events [35]. Clinical studies have shown that the reduction of
the hyperglycemia in patients with DMT1 and DMT2 is associated with a delay in the establishment and progression
of retinopathy, nephropathy, neuropathy and cardiac complications [138,139].
The main mechanism for endothelial dysfunction induced by diabetes mellitus and high extracellular D-glucose is
the oxidative stress resulting from the synthesis of ROS (Fig. 3) [35,140,141].

L-Arginine

High D-glucose
Vessel lumen

hCAT-1
p22

Cytoplasm

p4
7

NOX

eNOS

p6
7

O2.-

Protein kinase C

NO

L-Arginine

ONOOMAP kinases

H2O2

NFκB

mRNA hCAT-1
Sp1

Nox1

Nox4

SLC7A1

nucleus

Figure 3: Transcriptional regulation of NADPH oxidase and hCAT-1 in vascular endothelium exposed to high D-glucose. In
HUVEC exposed to high extracellular concentrations of D-glucose there is an increased activity of diacylglycerol-dependent
isoforms of protein kinases C, mitogen activated protein (MAP) kinases and transcriptional factors such as the nuclear factor
kappa B (NFkB), leading to increased NADPH oxidase (NOX) expression and activity mediated by an increase of promoter
activity of Nox1 and Nox4 genes in human fetoplacental vascular endothelium. A higher level of hydrogen peroxide (H2O2)
released from NOX activity leads to activation of the general transcription factor specific protein 1 (Sp1). This mechanism
induces an increase in the promoter activity of SLC7A1 gene, leading to increased human cationic amino acid transporter 1

106 An Overview of Association with Oxidative Stress

González et al.

(hCAT-1) expression and higher L-arginine transport and Nitric oxide (NO) synthesis from this amino acid via endothelial NO
synthase (eNOS). Concomitant to these cellular events, accumulation of nitrogen reactive species (including peroxynitrite
(ONOO-)) could be involved in high D-glucose triggered endothelial dysfunction and vascular pathology in the human
fetoplacental circulation [44].

It has been established that in vascular endothelium the major source of ROS is the activity of NOX [142], and the
intracellular O2- is one of the most powerful factors associated with reduction in NO bioavailability induced by D-glucose
[143]. In HUVEC, 33 mM D-glucose increases intracellular accumulation of ROS after 48 hours of exposure [144], while
25 mM D-glucose for 24 hours increases the accumulation of ROS and PKC activity [145]. Additionally, the increase in
the synthesis of ROS by high D-glucose has been associated with higher L-arginine transport; an effect blocked by coincubation with insulin or ascorbic acid in HUVEC. The experimental data reported in primary cultures of endothelial and
vascular smooth muscle cells from umbilical vessels and from placental vessels, show that high extracellular concentration
of D-glucose and gestational diabetes are associated with increased ROS synthesis with detrimental actions of NO, being
this mechanism a key factor to the development of endothelial dysfunction [2,6,44].
GESTATIONAL DIABETES
This is a syndrome characterized by glucose intolerance, leading to maternal hyperglycemia, first recognized during
pregnancy, associated with abnormal fetal development and perinatal complications, such as macrosomia, neonatal
hypoglycemia, and neuroconginitive and behavior disorders [72,146-149]. GD is one of the diseases of pregnancy
with highest incidence, depending on the diagnostic criteria used, varying between 3-8% of the total of pregnant
women in developing countries [150,151]. The main perinatal complications are late fetal mortality, fetal
macrosomia associated with delivery complications, metabolic alterations in the neonatal period such as
poliglobulia, hypoglycemia, hypocalcaemia. GD is characterized by abnormal regulation of the vascular tone in
placental and fetal tissues. GD also alters adenosine metabolism [152] and leas to abnormal regulation of the
vascular tone in placental and fetal tissues [153,154], a phenomenon associated with higher NO synthesis
[1,2,86,93]. GD alterations of fetal endothelial function, including reduced adenosine transport and increased NO
synthesis, are mimicked by exposure of HUVEC from normal pregnancies to elevated extracellular D-glucose (>5
mM, high D-glucose) [155], a condition associated with increased formation of O2- [156]. These findings are
thought important in diabetes mellitus where episodes of elevated D-glucose plasma levels can occurs leading to
endothelial dysfunction (Fig. 4).

Figure 4: Acute equilibrium between oxidant and antioxidant species in endothelial function. A perfect equilibrium between
oxidative (ROS) and nitrative (RNS) reactive species synthesis and bioactivity, and non-enzymatic and enzymatic antioxidant
mechanisms are required to maintain a normal function of the endothelium. This phenomenon is considered as the bases of a

Maternal and Fetal Vascular Oxidative and Nitrative Stress

An Overview of Association with Oxidative Stress 107

programming in uterus (‘fetal programming’) of a healthy state at adult life. When this equilibrium changes due to different
factors associated with diseases of pregnancy, such as preeclampsia (PE), preterm delivery (PTD), pre-gestational diabetes
mellitus (DM), gestational diabetes (GD) or intrauterine growth restriction (IUGR), a direct consequence is a reduced availability
of nitric oxide (NO), therefore limiting its several biological effects, due either to reduced synthesis or increased formation of
nitrative reactive species leading to protein nitration. The latter could ends in endothelial dysfunction, characteristic of the
mentioned diseases. Following this abnormal cell function an increased risk of developing diseases is expected during the adult
life of babies from women with pregnancies affected by these diseases. In this case the concept of fetal programming is validated
and becomes crucial. O2•-, superoxide anion; •OH, hydroxyl radical; ROO•, peroxide radicals; H2O2, hydrogen peroxide; NO-,
nitroxyl anion; ONOO-, peroxynitrite, VitC, vitamin C; VitE, vitamin E; GSH, reduced glutathione; SOD, superoxide dismutase;
GPx, glutathione peroxidase; CAT, catalase.

GD is associated with oxidative stress [157-159], where an overproduction of ROS and free radicals is
characteristic. In this phenomenon in GD, several enzymes are involved including NOX and XO [157], and
phenomena such as lipidic peroxidation products (i.e., malondialdehyde, thiobarbituric acid reactive subtances, lipid
hydroperoxide), which interrupt the electron flow in the mitochondrial respiratory chain [160-162], and protein
oxidation (i.e., carbonylation, nitration of tyrosine and methionine sulphoxide formation) leading to proteolytic
degradation [163]. In addition, RNS derived from NO leads to nitration and nitrosilation of several molecules,
including DNA nitration leading to apoptosis [164], protein nitration influencing enzyme activities [165], and lipid
nitration influencing several signaling pathways [166,167].
Studies in the last decade have proposed that GD alters adenosine transport via hENT1 and hENT2, and L-arginine
transport via hCAT-1 in HUVEC, suggesting that these pathological conditions alter cell signaling cascades
involving PI3K, PKC (most likely PKCα), NO and p42 and p44 MAPK (p42/p44mapk) [1,2,4,6,86,93,94]. One of the
consequences of the stimulation of this pathway is the activation of transcription factors inhibiting promoter activity
of SLC29A1 (for hENT1) leading to reduced transcript and protein abundance with the subsequent reduced
adenosine uptake. This could be a mechanism by which adenosine antioxidant properties could be facilitated since
increasing concentrations of this nucleoside are reported in the umbilical vein blood from GD [4,6]. Less is known
regarding expression and activity of hENT2 in this cell type, thus not really a clear contribution to this transport
system has been reported regarding adenosine actions as a protective factor in ROS and RNS generation and
biological effects in the fetoplacental circulation in this syndrome. It has been proposed that NO is not involved in
the modulation of hENT2 in HUVEC, but nothing is clear regarding the implications of the proposed signaling
pathway in the promoter activity of SLC29A2 in GD (and/or hyperglycemia). Interestingly, GD effects in the
microcirculation of the human placenta remain unknown [4, 6].
PRE-TERM DELIVERY (PTD)
This is the most frequent cause of neonatal mortality and one of the main causes of neurological damage, including
cerebral palsy. The risk of death is increasing not only in the prenatal period but also in the first year of postnatal
life. Excluding congenital malformations, 75% of perinatal deaths and 50% of neurological damage of infants are
associated directly to prematurity [168]. In this pathology the uterus exhibits limited forms to express a response to a
noxa or stimulus: uterine contractions (with the corresponding myometrium modifications) and altered structural
composition of the cervix (resulting in softening, effacement and dilatation). Around 30% of the PTD are secondary
to preterm rupture of the membranes (PROM) mainly due to maternal and fetal infectious compromise [169].
Biochemical mechanisms have been described involving metalloproteinases (MMPs) and interleukins, and more
recently it has been proposed an indirect role of the placental endothelium [170,171]. In addition, the existence of
mechanisms leading to spontaneous rupture of the membranes by unknown causes has been proposed. The period
between the rupture of membranes and labor, known as the latency period, could lead to increased risk of
intrauterine infection. These mechanisms are completely unknown in terms of cellular physiology of the
membranes, as well as cell dysfunction that could act at distance to modulate localized phenomena in the
membranes. One of the proposed alternatives is that PROM occurs after generation of a weakening area (a ‘weak
zone’) as a result of changes in the trans- and extra versus intracellular ionic equilibrium. This region, also called
‘zone of altered morphology (ZAM)’, has been observed in membranes at the cervix after term vaginal deliveries,
before labor and after preterm birth [172]. In addition, cytokines, prostaglandins and oxidative stress are proposed to
be involved mechanisms leading to PROM [173,174]. Increased synthesis of ROS is associated with apoptosis
[175], and cytochrome c release from mitochondria (marker of apoptosis) [173] is apparently largely mediated by

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González et al.

ROS action. In addition to this, oxidant stress caused by ROS and/or antioxidant depletion (for example adenosine
depletion) may damage amnion epithelium causing PROM [176]. It has been reported that antioxidant treatment
reduces lipopolysaccharide (LPS)-stimulated MMP-9 enzyme activity and glutathione peroxidase, glutathione
reductase, and SOD activity in amnion and chorion [177]. This phenomenon is associated with reduced antioxidant
enzyme activity leading to oxidative stress and collagen degradation.
CONCLUDING REMARKS
There are diverse evidences that are briefly discussed in this chapter that strongly suggest the relevance of proper
regulation of oxidative and nitrative stress in gestation to reduce the critical consequences in the development of
human pregnancy pathologies. Several aspects of pregnancy diseases, including PE, IUGR, diabetes mellitus as well
as PTD, point out to the general idea that oxidative/nitrative stress are highly interdependent mechanisms which will
be altered leading to endothelial dysfunction (see Fig. 4). These alterations could be crucial in the ‘programming’ of
the appearance of diseases in adult life. It is evident the need of a characterization of cellular and molecular
mechanisms involved in the etiology of these diseases of pregnancy and research focused in the signaling pathways
that are activated or inhibited in endothelium, vascular smooth muscle cells and syncytiotrophoblast from the
placenta is required. This has been the main topic of interest in recent scientific world congresses of related
societies, i.e., the International Federation of Placenta Associations (IFPA) [178], and the Developmental Origins of
Health and Diseases (DOHaD) Society [179]. The need of this future knowledge addressing some aspects
particularly associated with oxidative and nitrative stress of the etiology of these syndromes, will be valuable
information to understand vascular mechanisms supporting current and/or future therapeutic approaches for
treatment of patients (i.e, the baby and the mother) [6].
ACKNOWLEDGEMENTS
We thank the researchers at the Cellular and Molecular Physiology Laboratory (CMPL) and Perinatology Research
Laboratory (PRL) of the Division of Obstetrics and Gynecology at the Faculty of Medicine from Pontificia
Universidad Católica de Chile for their contribution in the production of the experimental data that has been cited
throughout the text. Authors also thank Mrs Ninoska Muñoz for excellent secretarial assistance, and the personnel of
the Hospital Clínico Pontificia Universidad Católica de Chile labor ward for supply of placentas.
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT 1110977, 1070865, 1080534, 11100192);
Programa de Investigación Interdisciplinario (PIA) from Comisión Nacional de Investigación en Ciencia y
Tecnología (CONICYT)(Anillos ACT-73), Chile; Dirección de Investigación Universidad de Concepción (DIUC
210.033.103-1.0), Concepción, Chile; Dirección de Investigación (DI-1339-07) and Vicerrectoría Académica
(Anillos ACT-73 postdoctoral research associate at CMPL-PRL, Pontificia Universidad Católica de Chile),
Universidad de Antofagasta, Chile; Fellowship Apoyo Realización de Tesis Doctoral from CONICYT AT23070213, AT-24090190. C Puebla, E Guzmán-Gutiérrez and E Muñoz hold CONICYT-PhD (Chile) fellowships.
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